Thin-film transistors (TFT) made of amorphous silicon for selecting pixels are used in a pixel circuit in an active-matrix liquid crystal display and an organic EL display. In order to drive the selecting TFTs, a driver circuit is provided at a periphery of the display. The driver circuit is composed of a logic device for outputting a driving pulse for turning the selecting TFT on or off.
The output voltage of the logic device embedded in a silicon circuit is usually smaller then the driving voltage of the TFT. In this case, a level shifter for boosting the output voltage of the logic device so as to match the output voltage to the driving voltage of the TFT is provided in a driver circuit.
FIG. 8 is a circuit configuration diagram of the conventional level shifter disclosed in the non-patent literature 1. The level shifter 500 illustrated in FIG. 8 includes transistors T1 to T6 which are n-type TFTs and capacitors C1 and C2. The level shifter 500 converts an input signal voltage Vin operating in a voltage amplitude between a fixed voltage VDD1 and a fixed voltage VSS1 to an output signal voltage Vout operating in a voltage amplitude between a fixed voltage VDD2 and a fixed voltage VSS2. With the circuit configuration illustrated in FIG. 8, the level shifter 500 is capable of reducing an output impedance, and performing a boosting operation for boosting a voltage to a voltage twice the original voltage or greater.
The patent literature 1 also discloses a level shifter which is composed of TFTs of a single-conduction type, holds amplitudes of an internal waveform and an output waveform by using an inverted signal of the input, or outputs amplitude larger than the amplitude of the input signal (performing a level shift operation). With this configuration, the patent literature 1 states that a clean internal waveform or output waveform can be achieved while maintaining low power consumption.
The patent literature 2 discloses a level shifter which is composed of TFTs of a single conduction type, avoids reduction in the output waveform or performs a level-shift operation using the inverted signal of the input and the diode connection of the TFT. With this, the patent literature 2 states that an output signal can be formed with low power consumption.